1. Field of the Invention
The present invention relates generally to pigging operations for cleaning pipelines, and more particularly relates to a pig storage and launching apparatus and method for pigging subsea pipelines.
2. Description of the Related Art
The production of paraffin, hydrates, and other detrimental materials from new oil and gas wells can not be accurately predicted before production begins. Subsea satellite oil wells are particularly susceptible to paraffin and hydrate blockage of the production pipeline because of the long pipeline lengths to a production manifold or platform and due to the cold temperatures on the sea floor. Oil producers are often faced with the need to clean pipelines that were expected to produce only clean, dry gas. Cleaning the pipelines with a pipeline pig is often the only available method to prevent paraffin buildup and subsequent blockage.
A common method of pigging a pipeline involves the use of a second pipeline, called a pigging loop, to send a pig to the end of the pipeline near the producing well. In many cases, no pigging loop exists because pigging needs were not envisioned when the well was completed.
The producing well is commonly connected to a single pipeline by a short pipe or hose, commonly called a "jumper," that has a connector on each end. Jumpers can be in various configurations. A common type of connecting jumper is called the "inverted U-jumper." The inverted U-jumper method of connecting a subsea well to a pipeline incorporates an upward facing male connector hub at a subsea tree and at the end of the pipeline. A U-jumper having a downward facing female connector hub at each end of a short pipe length is connected to the upward facing male connector hubs.
As subsea wells have moved into deeper and deeper waters, the costs associated with pigging a subsea pipeline have become an even greater issue to the oil producers. It is desirable to have a subsea pig launcher assembly that is simple to install and use, reliable, and cost effective. It is desirable that the subsea pig launcher assembly be capable of storing and launching a plurality of pigs over a period of time without retrieval to the surface. It is also desirable that the subsea pig launcher assembly maintains integrity of the pipeline fluid containment pressure boundary.